1. Field of the Invention
The present invention relates to an adjustable device for a chair, and more particularly to a depth-adjustable device for a chair that is free of the problem of wobble and noise.
2. Description of the Prior Art
Since different modern designs are used more and more widely in various chairs, various chairs with different adjustment mechanisms, such as chair with pneumatic height-adjustment structure, and spring type recliner, etc, have come into existence in our everyday life.
For example, a conventional depth-adjustable device for an office chair is shown in FIGS. 1 and 2, wherein a supporting board 10 for supporting the chair body (not shown) is slideably mounted on a railway 111 of a rail rack 11. The rail rack 11 is fixed to the chair foot 12, and a rotating handle 13 is pivotally mounted on the rail rack 11 and has a protruded block 131 engaged in a tooth groove 101 in a side of the supporting board 10. However, this conventional depth-adjustable device still has the following problems:
Firstly, since the supporting board 10 is slideably mounted on the square-shaped railway 111 of the rail rack 11, it will cause the shift of the center of gravity of the user when the weight of the person and the chair are applied to the supporting board 10. And the gap in the square-shaped railways 111 will make the rail rack 11 keep impacting the supporting board 10, causing wobble, and even worse, the wobble may cause the disengagement of the supporting board 10 out of the railway 111 of the rail rack 11.
Secondly, the rotating handle 13 is pivotally mounted on the rail rack 11 and has a protruded block 131 engaged in a tooth groove 101 in a side of the supporting board 10. However, the protruded block 131 and the tooth groove 101 are square-shaped in cross section, there will be a gap A between the protruded block 131 and the tooth groove 101, and this gap will also cause the supporting board to wobble or to disengage from the railway 111 of the rail rack 11.
Thirdly, no matter the supporting board 10 impacts the rail rack 11 or the protruded block 131 impacts the tooth groove 101, it will cause noise.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.